Self-healing material

ABSTRACT

A glass fiber-reinforced polymer composite includes a polymer matrix, a plurality of glass fibers embedded within the polymer matrix, a first hollow glass fiber containing a resin embedded within the polymer matrix, a second hollow glass fiber containing a catalyst suitable for curing the resin embedded within the polymer matrix. When damage occurs to such a composite, the glass fibers containing the resin and the catalyst are ruptured, resulting in their mixing together so that the resin is cured for repairing the ruptured location.

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/648,306, which is hereby incorporated by reference herein.

BACKGROUND INFORMATION

Composite materials are ideal for structural applications where highstrength-to-weight and stiffness-to-weight ratios are important. Weightsensitive applications, such as construction, aircraft, and spacevehicles, are primary consumers of composites, especiallyfiber-reinforced polymer matrix composites. However, their use islimited due to the difficulty in damage detection and repair, as well aslack of extended fatigue and impact resistance. One way to protectmaterial degradation is through the incorporation of a self-healingability.

To date, there has been significant research in self-healing polymericmaterials, and numerous studies, specifically in fiber-reinforcedpolymers. Polymer composites have been attractive candidates tointroduce the autonomic healing concept into modern day engineeringmaterials. A breakthrough in the study of self-healing materials wasreported in 2001 by a research group at University of Illinois (see S.R. White et al., “Autonomic healing of polymer composites,” Nature 409,pp. 794-797 (2001), which is hereby incorporated by reference herein).White et al. first introduced the incorporation of microcapsulescontaining a polymer precursor into the matrix material of anon-fiber-reinforced polymer composite for self-healing purposes. Thepolymer precursor was contained in microcapsules and embedded into thematrix. The matrix contained a randomly dispersed catalyst that wassupposed to react with the precursor flowing through any crack formeddue to damage and initiate polymerization. The polymer was then supposedto bond the crack face closed. The investigators overcame severalchallenges in developing microcapsules that were weak enough to beruptured by a crack but strong enough not to break during manufacture ofthe composite system. The researchers showed that it was possible torecover up to 75% of the maximum tensile strength of the virgincomposites. Successful work was done by Prof Bond's group. The use offunctional repair components stored in hollow glass fibers (“HGF”)placed with glass fiber/epoxy and carbon fiber/epoxy laminates caneffectively mitigate damage occurrence and restore mechanical strength(see R. S. Trask, G. J. Williams and I. P. Bond, “Bioinspiredself-healing of advanced composite structures using hollow glassfibres,” J. R. Soc. Interface 4, pp. 363-371 (2007), which is herebyincorporated by reference herein). If successful incorporation of theself-healing material into the fiber-reinforced composites (“FRP”) canbe achieved, the benefit is quite obvious. Those composites can servelonger with better performance. Self-healing materials embedded in theFRP composite or laminate showed considerable restoration of mechanicalproperties such as flexural strength, compressive strength, impactresistance, and a highly efficient recovery of matrix strength (see G.Williams, R. S. Trask and I. P. Bond, “Self-healing sandwich panels:Restoration of compressive strength after impact,” Composites Scienceand Technology 68, pp. 3171-3177 (2008) G. Williams, R. S. Trask and I.P. Bond, “A self-healing carbon fiber-reinforced polymer for aerospaceapplication,” Composites 38(6), pp. 1525-1532 (2007), which are herebyincorporated by reference herein).

Even though several methods have been suggested in autonomic healingmaterials, the concept of repair by bleeding of enclosed functionalagents has garnered wide attention by the scientific community. Theconcept of bleeding is also being considered for commercial purposes inthe aerospace industry. Achievements in the field of self-healingpolymers and polymer composites are far from satisfactory. Working outthe solutions would certainly push polymer sciences and engineeringforward.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a hollow glass fiber.

FIG. 1B illustrates a hollow glass fiber filled with a self-healingagent.

FIG. 1C illustrates a hollow glass fiber filled with as catalyst.

FIG. 2 illustrates an embodiment configured in accordance with thepresent invention.

FIG. 3 illustrates a testing procedure performed on an embodiment of thepresent invention.

FIG. 4 illustrates another testing procedure performed on an embodimentof the present invention.

FIG. 5 shows digital images of GFRP specimens produced in accordancewith embodiments of the present invention.

DETAILED DESCRIPTION

The inventors discovered that a vinyl ester resin and a methyl ethylketone peroxide (“MEKP”) catalyst can serve well as a self-healingmaterial system for FRP composites due, at least in part, to thefollowing advantages:

1. The vinyl ester can be cured at room temperature when contacted ormixed with a MEKP catalyst.

2. The viscosity of both the vinyl ester resin and the MEKP catalyst isvery low (<2,000 centipoises), which allows hollow glass fibers ormicrocapsules to be easily filled with each.

It was found that the vinyl ester resin/MEKP catalyst self-healingsystem can increase the service life of the panel and recoverperformance soon after initial damage.

According to aspects of the present invention, an example is hereinafterdescribed,

Part I. Base materials

1. Self-Healing Agent:

A vinyl ester resin (e.g., product designation Derakane 411-350) wascommercially obtained from Ashland, Inc. The MEKP catalyst wascommercially obtained from Crompton Corporation. Other resin systems,such as polyester and an appropriate catalyst may be used instead.

2. Hollow Glass Fiber:

FIG. 1A illustrates a cross-section of a hollow glass fiber 101. Largediameter hollow glass fibers were commercially obtained from SutterInstrument. The hollow glass fibers may be approximately 4 inches longwith an inner diameter (“1D”) of approximately 860 microns and an outerdiameter (“OD”) of approximately 1500 microns, which yields a hollownessfraction of approximately 33%. Other hollow glass fibers with differentdimensions or microcapsulates may be filled with self-healing agentsinstead.

3. Silicone Sealant:

Silicone sealant (e.g., commercially obtained from Master Bond, Inc.)may be used to seal the hollow glass fibers.

4. Fiberglass Fabric:

Product designation Hybon 2006 used to fabricate glass fiber-reinforcedpolymer (“GFRP”) panels was commercially obtained from PPG Industries.Other types of fibers, such as carbon fibers and synthetic fibers, maybe used instead.

5. Polyester Matrix:

The polyester matrix used to fabricate the GFRP panels was commerciallyobtained from Hexion (e.g., Hexion's 712 type polyester resin). Otherthermosetting resins, such as epoxy, vinyl ester, etc. may be usedinstead to perform the duty of the polymer matrix. The polymer matrixmay be enhanced with other polymers or fillers, such as carbonnanotubes, ceramic particles, graphite or graphene particles, etc.

Part 2. Fabricating GFRP Panels

1. Filling Hollow Glass Fibers with Self Healing Agent:

Referring to FIGS. 1B-1C, the hollow glass fibers 101 were first sealedat one end with silicone sealant 102. They were then immersed into thevinyl ester liquid in a vacuum chamber to allow the vinyl ester 203(i.e., self-healing agent or resin) to be drawn into the hollow glassfibers 101. Then the other ends of the hollow glass fibers were alsosealed with silicone sealant 102. The same process was also utilized tofill separate hollow glass fibers 101 with the MEKP catalyst 204.

2. Fabricating the GFRP Panels with Self-Healing Agent:

12″×12″×½″ GFRP panels were made based on two formulations. Formulation1 had a loading of 2.5% self-healing agent/catalyst compared to thetotal polyester matrix in the GFRP panels. Formulation 2 had a loadingof 5% self-healing agent/catalyst compared to the total polyester matrixin the GFRP panels. Five panels of each formulation were fabricated,Each panel contained 22 layers of e-glass fiber fabric. For each panel,the hollow glass fibers filled with self-healing agent were placedbetween the fourth and fifth, and eighteenth and nineteenth layers ofthe e-glass fiber fabric.

FIG. 2 illustrates an example of a GFRP panel 200 configured inaccordance with embodiments of the present invention. GFRP panel 200 isshown in a cross-section view of a GFRP composite integrated with hollowglass fibers filled with self-healing agent 203 and catalyst 204. Othersof glass fibers 201 typically used to make such composites are alsoshown embedded within the polymer (resin) matrix 201 of the GFRPcomposite. When damage occurs to such a panel, the glass fiberscontaining the self-healing agent and the catalyst are ruptured,resulting in their mixing together so that the agent is cued forrepairing the ruptured location.

Part 3. Ballistic Testing of the GFRP Panels with Self-Healing Agent

The GFRP panels were made by a hot pressing process. The polyester resinmixed with MEKP catalyst (1.5%) was poured onto each layer of thee-glass fiber fabric and put together to form a laminated structure. Itwas pressed at a temperature of approximately 250° F. degree forapproximately 30 minutes and cooled down to room temperature. They werethen made ready for V50 ballistic testing.

FIG. 3 shows a sketch of a typical panel and the planner placement ofeach shot for V50 ballistic testing. V50 tests were performed with a0.30 caliber FSP. V50 ballistic testing is the velocity at which 50percent of the shots go through and 50 percent are stopped by an armor.U.S. military standard MIL-STD-662F V50 Ballistic Test defines acommonly used procedure for this measurement.

Test Protocol

1. First Round of Shots: For each set, there were 3 shots per panel (15total shots per set). All of these were used to establish a V50 testresult (referred to as V50-A). The locations of these shots were nearthe dots marked “X” in FIG. 3.

2. Second Round of Shots: Within approximately 1 hour of the first roundof shots, two panels were shot 3 more times and one panel was shot 2more times near (approximately 1″ from) the original shots (this wasdone for both sets of panels). The purpose was to test the ballisticperformance of the panels before the vinyl ester cured. Those 8secondary shots were referred to as V50-B. Note, only 8 total shots wereused for this test, as the remaining 7 shots were used in the thirdround of V50 testing (described hereinafter).

3. Third Round of Shots: After approximately 1 week of the first roundof shots (V50-A), the remaining 7 shots were made near (approximately 1″from) the remaining original shots. The purpose was to allow the vinylester to be fully cured. Those 7 shots were used for another V50 test(referred to as V50-C) Thus all initial shots had a neighboring shotapproximately 1″ from the original. Each parcel had 6 shots 3 originaland 3 for either V50-B or V50-C testing.

Table 1 shows the V50 ballistic testing, results of the self-healingGFRP panels. The configuration for placement of hollow glass fibers(HGF) is shown below the table, where GF=glass fiber fabric.

TABLE 1 Loading of self- healing agent % (V50-A) (V50-B) (V50-C) 2.51585 1540 1614 5 1621 1544 1607

Placement of HGF:

GF/GF/GF/GF/HGF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/HGF/GF/GF/GF/GF

In summary:

1. V50-A is higher than V50-B. It was expected that after the firstballistic shot, the panel would be weakened;

2. V50-C is higher than V50-B and very close to the V50-A, which meansthat the self-healing agent/catalyst effectively heals the damaged areaof the panels after the first ballistic shot.

Another example now described showed that the mechanical properties ofthe GFRP composites can be recovered if the self-healing agent isembedded in the matrix. This example investigated the mechanicalbehavior before and after the self-healing agent is cured after impacttesting. Compression strength after impact for the GFRP panelsintegrated with self-healing agents was performed. The dimension of thespecimens for compression strength after impact testing is shown in FIG.4 (based on ASTM D7136 and ASTM D7137 testing). The panel thickness wasapproximately 0.2 inches, with 4 plies of the e-glass fiber fabricutilized. The self-healing layer will be placed in the middle of thespecimens Polyester resin (Hexion's 712 type polyester resin) ande-glass fiber (PPG's Hybon 2006 direct draw roving, 24 oz) were used asbase GFRP panel matrix materials for experimentation. Vinyl ester wasused as the self-healing agent and MEKP as catalyst. The GFRP specimenswere fabricated by being integrated with self-healing agent based on 2.5wt. % loading of the self-healing agent to resin matrix. The hollowglass fibers filled with self-healing agent and catalyst are placed inbetween the second and third plies of the e-glass fiber fabric. Forcomparison, also prepared were control GFRP panels for experimentation.FIG. 5 shows GFRP specimens used in the experimentation.

Fabricated were 4 GFRP samples. Each of the samples contained 12 GFRPspecimens. For the samples with self-healing agent, 6 specimens of eachsample were tested with impact. Then the compression strength afterimpact was performed within an hour. The remaining 6 specimens of eachsample were performed with compression strength after impact a weekafter the impact testing. The average data was given after each testing.For comparison and determining the self-healing efficiency, thecompression strength of the GFRP specimens (with no self-healing agent)without impact was also tested.

When the impact was performed, the hollow glass fibers were broken andthe self-healing agent and the catalyst were expelled from the fibers toreact with each other. The self-healing agent would barely react withthe catalyst within the first hour. However, the reaction would becompleted in a week.

A fully instrumented low velocity impact (Instron) machine was used toperform the impact at energy of 30 J.

The compression strength of the samples was the following:

GFRP samples without self-healing agent:

-   -   Compression strength (before impact): 50.0 MPa    -   Compression strength after impact: 38.3 MPa

GFRP samples with 2.5% self-healing agent:

-   -   Compression strength 1 hour after impact: 35.2 MPa    -   Compression strength 1 week after impact: 48.1 MPa It can be        seen that the compression strength observed one week after        impact (48.1 MPa) is significantly better than those tested        within an hour after impact (35.2 MPa), showing that the        self-healing agent plays an important role in healing the GFRP        panels after damage. The self-healing efficiency in this case is        96% and it almost recovers to the compression strength of the        undamaged GFRP (50.0 MPa), which is almost fully recovered.        Optimizing the loading of the self-healing agent may improve the        self-healing efficiency.

What is claimed is:
 1. A glass fiber-reinforced polymer compositecomprising: a polymer matrix; a plurality of glass fibers embeddedwithin the polymer matrix; a first hollow glass fiber embedded withinthe polymer matrix, the first hollow glass fiber containing a resin; anda second hollow glass fiber embedded within the polymer matrix, thesecond hollow glass fiber containing a catalyst suitable for curing theresin.
 2. The glass fiber-reinforced polymer composite as recited inclaim 1, wherein the resin comprises a vinyl ester.
 3. The glassfiber-reinforced polymer composite as recited in claim 1, wherein theresin comprises polyester.
 4. The glass fiber-reinforced polymercomposite as recited in claim 1, wherein the catalyst comprises methylethyl ketone peroxide.
 5. The glass fiber-reinforced polymer compositeas recited in claim 2, wherein the vinyl ester has a viscosity lowerthan 2,000 centipoises at room temperature.
 6. The glassfiber-reinforced polymer composite as recited in claim 3, wherein thepolyester has a viscosity lower than 2,000 centipoises at roomtemperature.
 7. The glass fiber-reinforced polymer composite as recitedin claim 4, wherein the methyl ethyl ketone peroxide has a viscositylower than 2,000 centipoises at mom temperature.
 8. The glassfiber-reinforced polymer composite as recited in claim 1, wherein thepolymer matrix comprises a thermosetting resin.
 9. The glassfiber-reinforced polymer composite as recited in claim 1, wherein thepolymer matrix is selected from the group consisting of polyester, vinylester, and epoxy.
 10. The glass fiber-reinforced polymer composite asrecited in claim 1, wherein the polymer matrix is a thermosetting resinreinforced with a filler.
 11. The glass fiber-reinforced polymercomposite as recited in claim 10, wherein the filler comprises carbonnanotubes.
 12. The glass fiber-reinforced polymer composite as recitedin claim 10, wherein the filler comprises ceramic particles.
 13. Theglass fiber-reinforced polymer composite as recited in claim 10, whereinthe filler comprises graphite particles.
 14. The glass fiber-reinforcedpolymer composite as recited in claim 10, wherein the filler comprisesgraphene particles.